Process for producing a styrene polymer and a catalyst for use therein

ABSTRACT

There are disclosed a process for producing a styrene polymer having a high degree of syndiotactic configuration at a reduced cost and an enhanced efficiency, and a catalyst to be used therefor which comprises (A) a specific transition-metal compound, (B) a specific coordination complex compound and (C) a compound having an alkyl group. The catalyst according to the present invention is inexpensive compared with the conventional catalyst containing aluminoxane as the major ingredient, and exhibits a high activity in polymerizing a styrenic monomer into styrene polymer with a high degree of syndiotacticity as well as a high yield and conversion rate.

This is a division of application Ser. No. 07/801,389, filed on Dec. 2,1991, now U.S. Pat. No. 5,272,229.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a process for producing a styrenepolymer and a catalyst for use therein. More particularly, it pertainsto a process for efficiently producing a styrene polymer having a highdegree of syndiotactic configuration in the stereochemical structure ofthe polymer main chain and to a catalyst to be used for the process.

2. Description of the Related Arts

It has recently been disclosed by the present inventors that a styrenepolymer having a syndiotactic configuration is obtained by polymerizinga styrenic monomer by the use of a catalyst comprising as primaryingredients a transition-metal compound, especially a titanium compoundand an alkylaluminoxane (Refer to Japanese Patent Application Laid-OpenNos. 187708/1987, 179906/1988, 241009/1988, etc.).

Methylaluminoxane, particularly suitable as an alkylaluminoxane isobtained usually by the reaction between trimethylaluminum and water.However, the above-mentioned reaction involves the problem that thereaction is difficult to put into practical production because of itsviolent reaction, and further suffers the disadvantage that in additionto requiring expensive trimethylaluminum as the starting material, anexcessively large amount of methylaluminoxane is required as a componentof the catalyst as compared with the quantity of a transition metal,thus causing an extremely expensive catalyst.

There has recently been reported that a polymerization catalyst notcontaining aluminoxane is capable of polymerizing α-olefin(principally,ethylene), by R. Taube (J. Organomet. Chem. C9-C11, 347 (1988)), H.Turner (J. Am. Chem. Soc. 111, 2728 (1989)), R. F. Jordan (Organomet.8,2892 (1989)), etc. Nevertheless, investigation has not yet been madeon a polymerization catalyst not containing aluminoxane for thepolymerization of styrenic monomer, leaving the problem that styrenicmonomer, different from α-olefin, is likely to be polymerized into anatactic polymer in the presence of a cationic species.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a process foreffectively producing a styrene polymer having a high degree ofsyndiotactic configuration.

It is another object of the present invention to provide a catalystcapable of efficiently polymerizing a styrenic monomer into a styrenepolymer having a high degree of syndiotactic configuration without theuse of expensive aluminoxane required in a large quantity.

Other objects of the present invention will be obvious from the text ofthe specification hereinafter disclosed.

As the result of intensive research and investigation made by thepresent inventors for the purpose of attaining the above-describedobject, it has been found that the use of a catalyst combinationcomprising a specific transition-metal compound and a specific salt iscapable of efficiently producing the objective styrene polymer having ahigh degree of syndiotactic configuration by virtue of its markedlyimproved activity. The present invention has been accomplished on thebasis of the aforestated finding and information.

Specifically, the present invention provides a catalyst for theproduction of a styrene polymer having a high degree of syndiotacticconfiguration which comprises (A) a transition-metal compound not havingany of metal-hydrogen bonds, metal-carbon σ-bonds and metal-siliconσ-bonds, (B) a coordination complex compound comprising a cation and ananion in which a plurality of radicals are bonded to a metal and (C) acompound having an alkyl group. The present invention also provides aprocess for producing a styrene polymer which comprises polymerizingstyrene and/or a styrene derivative in the presence of the foregoingcatalyst.

DESCRIPTION OF PREFERRED EMBODIMENTS

The catalyst according to the present invention comprises as the primaryingredients, components (A), (B) and (C). The component (A) is atransition-metal compound without any of metal-hydrogen bonds,metal-carbon σ-bonds and metal-silicon σ-bonds. As transition metals,mention may be made of the metals belonging to Group III, IV, V or VI inthe Periodic Table and Lanthanide Series, and among them, Group IVmetals including titanium, zirconium and hafnium are preferable, andtitanium is most suitable. The suitable transition-metal compound isthat having oxygen, sulfur, nitrogen, halogen (chlorine, bromine,fluorine) or the like together with the aforementioned transition metal.

These elements are incorporated into the compounds in a variety offorms, for example, oxygen is incorporated as an alkoxy or aryloxy (OR;R is an alkyl group or aryl group), an ester (COOR; R represents thesame as above), acetylacetonate (AcAc) or the like, sulfur as alkylthioor arylthio (SR: R represents the same as above) or the like andnitrogen as alkylamino, arylamino, dialkylamino, diarylamino (NHR, NR₂ :R represents the same as above) or the like.

A transition-metal compound of the component (A) can be represented bythe general formula (I)

    M.sup.1 R.sup.1 R.sup.2 R.sup.3 R.sup.4                    (I)

wherein M¹ is a transition metal; R¹, R², R³ and R⁴ are each an alkoxygroup, aryl group, aryloxy group, halogen atom, thiol group, arylthiogroup, amino group, alkylamino group, acetylacetonate group, chelatingagent or ligand of conjugated π-electron system such as cyclopentadienylgroup, substituted cyclopentadienyl group, indenyl group or fluorenylgroup. In addition to the combinations of the above, the compound may bea bidentate coordination complex compound such as2,2'-thiobis(4-methyl-6-tert-butylphenyl)titanium diisopropoxide;2,2'-thiobis(4-methyl-6-tert-butylphenyl)titanium dimethoxide or thelike.

The preferable compound is that in which one of R¹, R², R³ and R⁴ is aligand of conjugated π-electron system. Specific examples of thetransition-metal compound represented by the general formula (I) include

cyclopentadienyltitanium trimethoxide,

cyclopentadienyltitanium triethoxide,

pentamethylcyclopentadienyltitanium trimethoxide,

pentamethylcyclopentadienyltitanium triethoxide,

cyclopentadienyltitanium trichloride,

pentamethylcyclopentadienyltitanium trichloride,

cyclopentadienylmonomethoxytitanium dichloride,

cyclopentadienyldimethoxytitanium monochloride,

pentamethylcyclopentadienylmonomethoxytitanium dichloride,

cyclopentadienyltitanium triphenoxide,

pentamethylcyclopentadienyltitanium triphenoxide,

cylopentadienyltitanium monochloride,

pentamethylcyclopentadienyltitanium monochloride,

cyclopentadienylmonophenoxytitanium dichloride,

pentamethylcyclopentadienylmonophenoxytitanium dichloride,

cyclopentadienyltribenzyltitanium,

pentamethylcyclopentadienyltribenzyltitanium, indenyltitanium

trichloride, indenyltitanium trimethoxide, indenyltitanium

triethoxide, and indenyltribenzyltitanium, etc.

The component (B) according to the present invention is a coordinationcomplex compound comprising a cation and an anion in which a pluralityof radicals are bonded to a metal. A variety of such coordinationcomplex compounds are available, and those represented by the followinggeneral formula (II) or (III) are preferably employed:

    ([L.sup.1 -H].sup.g+).sub.h ([M.sup.2 X.sup.1 X.sup.2 . . . X.sup.n ].sup.(n-m)-).sub.i                                       (II)

or

    ([L.sup.2 ].sup.g+).sub.h ([M.sup.3 X.sup.1 X.sup.2 . . . X.sup.n ].sup.(n-m)-).sub.i                                       (III)

wherein L² is M⁴, R⁵ R⁶ M⁵ or R⁷ ₃ C as hereinafter described; L₁ is aLewis base; M² and M³ are each a metal selected from Groups V to XV ofthe Periodic Table; M⁴ is a metal selected from Groups VIII to XII ofthe Periodic Table; M⁵ is a metal selected from Groups VIII to X of thePeriodic Table; X¹ to X^(n) are each a hydrogen atom, dialkylaminogroup, alkoxy group, aryloxy group, alkyl group having 1 to 20 carbonatoms, aryl group having 6 to 20 carbon atoms, alkylaryl group,arylalkyl group, substituted alkyl group, organometalloid group orhalogen atom; R⁵ and R⁶ are each a cyclopentadienyl group, substitutedcyclopentadienyl group, indenyl group or fluorenyl group; R⁷ is an alkylgroup; m is the valency of each of M² and M³, indicating; an integer of1 to 7; n is an integer of 2 to 8; g is the ion valency of each of [L¹-H] and [L² ], indicating an integer of 1 to 7; h is an integer of 1 ormore; and i=hxg/(n-m).

Specific examples of M² and M³ include B, Al, Si, P, As, Sb, etc.; thoseof M⁴ include Ag, Cu, etc.; and those of M⁵ include Fe, Co, Ni, etc.Specific examples of X¹ to X^(n) include dialkylamino group such asdimethylamino and diethylamino; alkoxyl group such as methoxy,, ethoxyand n-butoxy; aryloxy group such as phenoxy, 2,6-dimethylphenoxy andnaphthyloxy; alkyl group having 1 to 20 carbon atoms such as methyl,ethyl, n-propyl, iso-propyl, n-butyl, n-octyl and 2-ethylhexyl; arylgroup having 6 to 20 carbon atoms, alkylaryl group or arylalkyl groupsuch as phenyl, p-tolyl, benzyl, pentafluorophenyl,3,5-di(trifluoromethyl)phenyl, 4-tert-butylphenyl, 2,6-di-methylphenyl,3,5-dimethylphenyl, 2,4-dimethylphenyl and 1,2-dimethylphenyl; halogensuch as F, Cl, Br and I; and organometalloid such as pentamethylantimonygroup, trimethylsilyl group, trimethylgermyl group, diphenylarsinegroup, dicyclohexylantimony group and diphenylboron group. Specificexamples of substituted cyclopetnadienyl of R⁵ and R⁶ includemethylcyclopentadienyl, butylcyclopentadienyl andpentamethylcyclopentadienyl.

Among the compounds represented by the general formula (II) or (III),specific examples of preferably usable compounds include, as thecompound of general formula (II), triethylammonium tetraphenylborate,tri(n-butyl)ammonium tetraphenylborate, trimethylammoniumtetraphenylborate, triethylammonium tetra(pentafluorophenyl)borate,tri(n-butyl)ammonium tetra(pentafluorophenyl)borate, triethylammoniumhexafluoroarsenate, etc., and as the compound of general formula (III),pyridinium tetra(pentafluorophenyl)borate, pyrroliniumtetra(pentafluorophenyl)borate, N,N-dimethylaniliniumtetra(pentafluorophenyl)borate, methyldiphenylammoniumtetra(pentafluorophenyl)borate, ferrocenium tetraphenylborate,dimethylferrocenium tetra(pentafluorophenyl)borate, ferroceniumtetra(pentafluorophenyl)borate, decamethylferroceniumtetra(pentafluorophenyl)borate, acetylferroceniumtetra(pentafluorophenyl)borate, formylferroceniumtetra(pentafluorophenyl)borate, cyanoferroceniumtetra(pertafluorophenyl)borate, silver tetraphenylborate, silvertetra(pentafluorophenyl)borate, trityltetraphenylborate,trityltetra(pentafluorophenyl)borate, silver hexafluoroarsenate, silverhexafluoroantimonate, silver tetrafluoroborate, etc.

The catalyst according to the present invention further comprises (C) acompound having an alkyl group. A variety of compounds having an alkylgroup are available, and aluminum compounds having an alkyl grouprepresented by the general formula (IV) are exemplified.

    R.sup.8.sub.m Al(OR.sup.9).sub.n X.sub.3-m-n               (IV)

wherein R⁸ and R⁹ independently are each an alkyl group having 1 to 8,preferably 1 to 4 carbon atoms; X is a hydrogen atom or a halogen atom;m satisfies the relation 0<m<3, desirably m=2 or 3, more desirably m=3;and n satisfies the relation 0≦n<3, desirably n=0 or 1.

Also exemplified are magnesium compounds having an alkyl grouprepresented by the general formula (V)

    R.sup.8.sub.2 Mg                                           (V)

wherein R⁸ represents the same as above, zinc compounds having an alkylgroup represented by the general formula (VI)

    R.sup.8.sub.2 Zn                                           (VI)

wherein R⁸ represents the same as above, and the like.

The above-mentioned compounds having an alkyl group are desirablyaluminum compounds having an alkyl group, more desirablytrialkylaluminum compounds and dialkylaluminum compounds. Examples of(C) the compounds having an alkyl group to be used in the presentinvention include trialkylaluminum such as trimethylaluminum,triethylaluminum, tri-n-propylaluminum, triisopropylaluminum,tri-n-butylaluminum, triisobutylaluminum and tri-tert-butylaluminum;dialkylaluminum halide such as dimethylaluminum chloride,diethylaluminum chloride, di-n-propylaluminum chloride,diisopropylaluminum chloride, di-n-butylaluminum chloride,diisobutylaluminum chloride and di-tert-butylaluminum chloride;dialkylaluminum alkoxide such as dimethylaluminum methoxide anddimethylaluminum ethoxide; dialkylaluminum hydride such asdimethylaluminum hydride, diethylalumium hydride and diisobutylaluminumhydride; dialkylmagnesium such as dimethylmagnesium, diethylmagnesium,di-n-propylmagnesium and diisopropylmagnesium; and dialkylzinc such asdimethylzinc, diethylzinc, di-n-propylethylzinc and diisopropylzinc, andthe like.

The catalyst of the present invention which comprises the abovestatedcomponents (A), (B) and (C) as primary ingredients can be prepared byvarious methods including:

(1) a method in which the reaction product of the components (A) and (B)is added with the component (C) to produce the catalyst, which is thenbrought into contact with a monomer or monomers to be polymerized;

(2) a method in which the reaction product of the components (A) and (C)is added with the component (B) to produce the catalyst, which is thenbrought into contact with a monomer or monomers to be polymerized;

(3) a method in which each of the components (A), (B) and (C) is addedto a monomer or monomers to be polymerized one by one in any order. Thereaction product of the components (A) and (B) may be isolated andpurified in advance.

The addition or contact of the above-mentioned components (A), (B) and(C) may be carried out at the polymerization temperature of at 0° to100° C.

As described hereinbefore, the catalyst according to the presentinvention exhibits a high activity for the production of a styrenepolymer having a high degree of syndiotactic configuration. Hence, thepresent invention further provides a process for producing a styrenepolymer having a high degree of syndiotactic configuration by the use ofthe abovestated catalyst.

The production of a styrene polymer according to the process of thepresent invention is put into practice by polymerizing or copolymerizingstyrenic monomer/s such as styrene and/or a styrene derivativeexemplified by an alkylstyrene, alkoxystyrene, halogenated styrene,vinyl benzoate ester, etc. in the presence of the catalyst comprisingthe foregoing components (A), (B) and (C) as essential ingredients. Asdescribed above, there are available a variety of methods for bringingthe catalyst of the present invention into contact with a styrenicmonomer or monomers.

The polymerization of a styrenic monomer or monomers may be carried outby means of bulk polymerization or solution polymerization by the use ofan aliphatic hydrocarbon solvent such as pentane, hexane or heptane, analicyclic hydrocarbon solvent such as cyclohexane or an aromatichydrocarbon solvent such as benzene, toluene or xylene. Thepolymerization temperature is not specifically limited, but is usuallyin the range 0° to 105° C., preferably 20° to 100° C.

The molecular weight of the styrene polymer to be obtained can beeffectively modified by means of polymerization reaction in the presenceof hydrogen.

The styrene polymer thus obtained possesses a high degree ofsyndiotactic configuration. Here, the styrene polymer having a highdegree of syndiotactic configuration means that its stereochemicalstructure is mainly of syndiotactic configuration, i.e. thestereostructure in which phenyl groups or substituted phenyl group asside chains are located alternately at opposite directions relative tothe main chain consisting of carbon-carbon bonds. Tacticity isquantitatively determined by the nuclear magnetic resonance method (¹³C-NMR method) using carbon isotope. The tacticity as determined by the¹³ C-NMR method can be indicated in terms of proportions of structuralunits continuously connected to each other, i.e., a diad in which twostructural units are connected to each other, a triad in which threestructural units are connected to each other and a pentad in which fivestructural units are connected to each other. "The styrene polymershaving a high degree of syndiotactic configuration" as mentioned in thepresent invention means polystyrene, poly(alkylstyrene),poly(halogenated styrene), poly(alkoxystyrene), poly(vinylbenzoate), themixtures thereof, and copolymers containing the above polymers as maincomponents, having such a syndiotacticity that the proportion of racemicdiad is at least 75%, preferably at least 85%, or the proportion ofracemic pentad is at least 30%, preferably at least 50%. Thepoly(alkylstyrene) include poly(methylstyrene), poly(ethylstyrene),poly(isopropylstyrene), poly(tert-butylstyrene), etc., poly(halogenatedstyrene) include, poly(chlorostyrene), poly(bromostyrene), andpoly(fluorostyrene), etc. The poly(alkoxystyrene) include,poly(methoxystyrene), poly(ethoxystyrene), etc.

The most desirable styrene polymers are polystyrene,poly(p-methylstyrene), poly(m-methylstyrene), poly(p-tert-butylstyrene),poly(p-chlorostyrene), poly(m-chlorostyrene), poly(p-fluorostyrene), andthe copolymer of styrene and p-methylstyrene.

The styrene polymer obtained according to the process of the presentinvention is that with a high degree of syndiotacticity usually having aweight-average molecular weight of 10,000 to 3,000,000, preferably100,000 to 1,500,000 with a number-average molecular weight of 5,000 to1,500,000, preferably 50,000 to 1,000,000. Moreover, the styrene polymerhaving an exceptionally high degree of syndiotacticity as well as anextremely high purity can be obtained by the steps of deashing treatmentof the polymer thus obtained, as required, with a washing agentcontaining hydrochloric acid, etc.; additional washing; drying underreduced pressure; cleaning with a solvent such as methyl ethyl ketonefor removing solubles therein; and treatment of the insolubles thusobtained by the use of chloroform, etc.

The styrene polymer with a high degree of syndiotacticity has a meltingpoint of 160° to 310° C. and is remarkably superior to the conventionalstyrene polymer with an atactic configuration in terms of heatresistance.

The catalyst according to the present invention is inexpensive ascompared with the conventional catalyst comprising an aluminoxane as aprimary ingredient, and exhibits a high activity for the production of astyrene polymer having a high degree of syndiotactic configuration.According to the process of the present invention, therefore, asyndiotactic styrene polymer is obtained at a reduced production costand with enhanced efficiency.

The present invention will be described in more detail with reference tothe following nonlimiting Examples and Comparative Examples.

EXAMPLE 1

Into a 500 ml reaction vessel, 200 ml of styrene was placed with heatingto 70° C., and then, 5 ml of a mixed contact solution of 0.005 mmol ofpentamethylcyclopentadienyltitanium trimethoxide, 0.005 mmol of1,1'-dimethylferrocenium tetra(pentafluorophenyl)borate and 0.05 mmol oftriisobutylaluminum in toluene was added thereto, and polymerization wascarried out at 70° C. for 4 hours. After the reaction, polymerizationwas arrested with methanol, and the mixture was deashed withhydrochloric acid-methanol, washed with methanol, and dried to give 42.3g of polymer. The polymer was subjected to extraction with a Soxhletextractor using methyl ethyl ketone as a solvent to give an extractionresidue (methyl ethyl ketone insoluble portion; MIP) of 97% by weight.It was confirmed that the resultant polymer was a syndiotacticpolystyrene having a melting point (Tm) of 268° C. and a weight-averagemolecular weight of 750,000.

EXAMPLE 2

The procedure in Example 1 was repeated except that 0.2 mmol oftriisobutylaluminum was added instead of 0.05 mmol of the same. Thepolymer was obtained in a yield of 52.0 g as an extraction residue (MIP)of 98% by weight, and was a syndiotactic polystyrene having a meltingpoint (Tm) of 268° C. and a weight-average molecular weight of 570,000.

The catalyst according to the present invention is inexpensive ascompared with the conventional catalyst comprising an aluminoxane as aprimary ingredient, and exhibits a high activity for the production of astyrene polymer having a high degree of syndiotactic configuration.According to the process of the present invention, therefore, asyndiotactic styrene polymer is obtained at a reduced production costand with an enhanced efficiency.

EXAMPLE 3

The procedure of Example 1 was repeated except that1,2,4-trimethylcyclopentadienyltitanium trimethoxide was used in placeof pentamethylcyclopentadienyltitanium trimethoxide. The polymer wasobtained in a yield of 24.3 g as an extraction residue (MIP) of 96% byweight, and was a syndiotactic polystyrene having a melting point (Tm)of 266° C. and a weight-average molecular weight of 117,000.

EXAMPLE 4

The procedure of Example 1 was repeated except thatcyclopentadienyltitanium trimethoxide was used in place ofpentamethylcyclopentadienyltitanium trimethoxide and 0.02 mmol oftriisobutylaluminum was added instead of 0.05 mmol of the same. Thepolymer was obtained in a yield of 36.3 g as an extraction residue (MIP)of 16.3% by weight, and was a syndiotactic polystyrene having aweight-average molecular weight of 53,000.

EXAMPLE 5

The procedure of Example 1 was repeated except thatpentamethylcyclopentadienyltitanium trichloride was used in place ofpentamethylcyclopentadienyltitanium trimethoxide and 0.02 mmol oftriisobutylaluminum was added instead of 0.05 mmol of the same. Thepolymer was obtained in a yield of 47.8 g as an extraction residue (MIP)of 53.7% by weight, and was a syndiotactic polystyrene having aweight-average molecular weight of 537,000.

EXAMPLE 6

The procedure of Example 1 was repeated except that the transition metalrepresented by the formula A ##STR1## was used in place ofpentamethylcyclopentadienyltitanium trimethoxide and 0.02 mmol oftriisobutylaluminum was used instead of 0.05 mmol of the same. Thepolymer was obtained in a yield of 3.8 g as an extraction residue (MIP)of 52.4% by weight, and was a syndiotactic polystyrene having aweight-average molecular weight of 146,000.

EXAMPLE 7

The procedure of Example 1 was repeated except that 0.02 mmol oftrimethylaluminum was used in place of 0.05 mmol of triisobutylaluminum.The polymer was obtained in a yield of 74.2 g as an extraction residue(MIP) of 94.9% by weight, and was a syndiotactic polystyrene having aweight-average molecular weight of 1,238,800.

EXAMPLE 8

The procedure of Example 7 was repeated except that trimethylaluminum,pentamethylcyclopentadienyltitanium trimethoxide and1,1'-dimethylferrocenium tetra(pentafluorophenyl)borate were each addedin that order. The polymer was obtained in a yield of 83.2 g as anextraction residue (MIP) of 89.4% by weight, and was a syndiotacticpolystyrene having a weight-average molecular weight of 1,123,000.

EXAMPLE 9

The procedure in Example 1 was repeated except that polymerizationtemperature was 95° C. instead of 70° C. The polymer was obtained in ayield of 23.8 g as an extraction residue (MIP) of 97% by weight and wasa syndiotactic polystyrene having a melting point (Tm) of 268° C. and aweight average molecular weight of 250,000.

Comparative Example 1

The procedure of Example 1 was repeated except that triisobutylaluminumwas not used. As a result, no polymer was obtained.

What is claimed is:
 1. A catalyst, which comprises:as primaryingredients, (A) a transition metal compound of formula (I): M¹ R¹ R² R³R.sup. 4, wherein M¹ is titanium; R¹, R², R³ and R⁴ are each acyclopentadienyl group, a substituted cyclopentadienyl group, alkoxy orhalogen; (B) a coordination complex compound of the formula:

    ([L.sup.2 ].sup.g+).sub.h ([M.sup.3 X.sup.1 X.sup.2 . . . X.sup.n ].sup.(n-m)-).sub.i

wherein L² is M⁴, which is a metal selected from Groups VIII to XII ofthe Periodic Table R⁵ R⁶ M⁵ or R⁷ ₃ C, wherein M⁵ is a metal selectedfrom Groups VIII to X of the Periodic Table, R⁵ and R⁶ are each acyclopentadienyl group, a substituted cyclopentadienyl group, indenyl orfluorenyl and R⁷ is alkyl; M³ is boron; X¹ to X^(n) are each a memberselected from the group consisting of phenyl, p-tolyl, benzyl,4-tert-butylphenyl, 2,6-dimethylphenyl, 3,5-dimethylphenyl,2,4-dimethylphenyl, 1,2-dimethylphenyl, pentafluorophenyl, and3,5-di(trifluoromethyl) phenyl; m is the valency of M³ and is an integerof 1 to 7; n is an integer of 2 to 8; g is the ion valency of [L² ],wherein the integer of the valency state ranges from 1 to 7; h is aninteger of 1 or more and i=hxg/(n-m); and (C) a compound selected fromthe group consisting of R⁸ ₃ Al, R⁸ ₂ Mg and R⁸ ₂ Zn, wherein R⁸ is analkyl group of 1 to 8 carbon atoms.
 2. The catalyst of claim 1, whereinsaid compound (C) is an alkylaluminum compound.